With respect to a device in which a high-magnification calibrating apparatus with a narrow calibration range is combined with another calibrating apparatus in order to position the calibrating range in any desired location, this invention provides a means of determining and compensating for the discrepancies between the calibration positions of both apparatuses, and, more specifically, it relates to a composite device comprising a scanning tunnelling microscope (STM) and an optical microscope or scanning electron microscope (SEM).
In a conventional scanning tunnelling microscope, the calibration sample and the needle are observed obliquely using a stereoscopic microscope or the like. Because the sample is observed obliquely in this way, not all of the sample surface is in focus, and, furthermore, because a stereoscopic microscope has a low magnification of about 200 times at maximum, it has been extremely difficult to guide the STM needle to the location of the sample to be observed with a precision better than 10.mu.. Thus, with the STM, the intended sample location is sought by repeating an operation whereby the largest picture frame is scanned, the stage is conveyed forwards and the STM is scanned again. However, this method takes up a considerable amount of time and is inconvenient for practical purposes.
A STM device has a resolution of 2 to 3 .ANG. in the lateral direction and a resolution of 0.1 .ANG. or more in the longitudinal direction but a narrow scanning region of about 10-12.mu. at most, and the field of view is insufficient to seek a specific position in a sample using the STM alone. There is therefore a need to combine it with a microscope with a wider field of view and, in order to link the fields of view of the two, it is necessary to link the needle position of the STM and the optical axis of the other microscope.
Further, the STM has a problem in that the needle is a consumable article and is frequently changed so that it needs to be readily positionable. This invention has been designed to overcome such disadvantages and aims to provide a STM device which has a sample stage incorporating a standard sample within the device, has a mechanism for aligning the optical axis of an optical microscope on the central lines of this standard sample, has a mechanism which takes in the STM image and ascertains which position of the standard sample it corresponds to from this STM image, and has a mechanism which calculates the positional relationship between the optical axis and the STM needle and makes an accurate movement to this amount.